A voice service in a Long Term Evolution (LTE) network is referred to as Voice over Long Term Evolution (VoLTE). Currently, more operators start to use VoLTE commercially, and more user terminals can support the VoLTE service. VoLTE is a voice technology based on IP (Internet Protocol) data transmission, and all services are carried in an LTE network. In this way, data and voice services can be carried in the same network.
The LTE network is an all-IP network. Like a data service, a voice service in the LTE network is carried on an IP-based bearer. VoLTE voice session signaling is transmitted between an IMS Internet Protocol multimedia subsystem (IMS) network and user equipment by using a bearer (a value of quality of service class identifier QCI (quality of service class identifier) of the bearer is usually 5), and some other services may also be transmitted between the IMS network and the user equipment by using the bearer, for example, an SMS short message service) service and an RCS (Rich Communication Suite) service.
The prior art has the following disadvantage: when network resources are limited, a setup delay of an existing VoLTE voice session is increased.